It is well known that androgens under the influence of the hypothalmo-hypophyseal axis play a vital role in the development and regulation of male infertility. Yet, precise information about the mechanisms of androgen support for spermatogenesis and sperm metabolism are often lacking. The mechanisms supporting the specific endocrine microenvironments inside these seminiferous and epididymal tubules, for example, are virtually unexplored; thus, little is known about the control of the androgen milieu to which developing germ cells, maturing spermatozoa, and the reproductive tract epithelia are exposed. Sperm development and maturation occur inside the blood-testis and blood-epididymal barriers and information about the control of the intraluminal environment cannot be obtained by the common studies of tissue extracts or vascular fluids. This application proposes to investigate the little-understood aspects of the endocrine physiology of the seminiferous and epididymal tubules: 1) the rate and mechanisms of androgen transport from the interstitium to the lumen of the seminiferous and epididymal tubules; and 2) the influence of gonadotropins and prolactin on steroid transport across the seminiferous and epididymal epithelia. The specialized techniques of in vivo micropuncture and in vivo microperfusion of male rat reproductive tract tubules will be used to perform these studies. This information is necessary to the understanding of 1) Steroli cell control of the intraluminal environment of the seminiferous tubules, 2) the biological usefulness of ABP secretion by Sertoli cells, 3) the role of epididymal principal cells in controlling the intraluminal androgen microenvironment, and 4) the role of pituitary hormones in the control of seminiferous tubule and epididymal tubule function.